Carboxymethyl cellulose, polyacrylic acid or its salt, and natural gum, for example, have been conventionally known as a gelling agent for alkaline batteries. The gelling agent for alkaline batteries needs to be stable over a long period of time also under strong alkaline conditions of an alkaline electrolyte. In recent years, carboxyl group-containing polymers that have, as a main monomer component, α,β-unsaturated carboxylic acid-type compound—in particular, (meth)acrylic acid and its salt—have been mainly used.
Various performances are required for the gelling agent for alkaline batteries. One of the required performances is shock resistance for protecting the inside of the batteries upon application of external force thereto. As a method for improving shock resistance, there is proposed a method with a swellable carboxyl group-containing polymer that swells upon absorption of an alkaline electrolyte (see Patent Document 1).
On the other hand, there have been demanded performances with which appropriate viscosity, electrolyte retainability, and stability are imparted to an alkaline electrolyte, and which improves dispersibility of various metals to be added to an alkaline electrolyte. Proposed as a method for improving dispersibility is a method with a carboxyl group-containing polymer that dissolves in an alkaline electrolyte and serves as a paste gel (see Patent Document 2).
Since the carboxyl group-containing polymer is usually a fine powder, undissolved lumps tend to occur when the polymer is added to an alkaline electrolyte (alkaline solution). A method for adding a carboxyl group-containing polymer with high-speed stirring of an alkaline electrolyte to prevent formation of undissolved lumps is proposed. However, since the alkaline electrolyte embraces air under stirring and upon dissolution, a gel including a large amount of air (including bubbles) in the alkaline electrolyte is formed. When a gel includes bubbles, it takes time and effort to remove the bubbles from the gel, and thus it is difficult to remove all the bubbles. Also, problematically, the gel including bubbles increases its volume by the bubbles, and the filling rate to batteries per unit volume decreases, leading to deterioration in battery performances.    Patent Document 1: Japanese Kokai Publication Hei-3-89458 (JP-A H03-89458)    Patent Document 2: Japanese Kokai Publication 2003-123763 (JP-A 2003-123763)